Automated fluid injection devices, particularly automated needle syringes, have gained wide acceptance by industry, universities, and by the scientific and medical communities. This is due in large part to the advantages offered by modern data gathering techniques, and consequent reduction in operating manpower without loss in accuracy.
Automated fluid injection devices of such character are capable of dispensing very small, accurately measured quantities of fluid specimens on the order of a few microliters, or very small fractions of a microliter, e.g. from about 0.01 to about 5 microliters, or fractional parts thereof. In the operation of such fluid injection devices, septum covered vials charged with portions of a fluid specimen are transported via a magazine to a station adjacent a probe assembly, the probe assembly picks up a specimen from a vial and a portion of the fluid specimen is conveyed via action of the probe assembly to the syringe. Within the barrel of the syringe, a quantity of the fluid specimen is measured out and injected via the dispensing end of the syringe into the inlet of the analytical instrument. Such a device is described, e.g., in U.S. Pat. No. 4,044,616.
Albeit very small quantities of fluid specimens can be measured out within the barrel of the syringe, and accurately injected, often hardly enough of a given total fluid specimen is available for such purpose. It is one thing to measure out and inject a given specific quantity of a fluid specimen into an analytical instrument, and it is another to effect virtually total delivery of a minimal available amount of a fluid specimen for such purpose. Unavoidably, a certain amount of the total of a given specimen never reaches the barrel of the syringe. Inevitably, it appears, a major portion of a given fluid specimen is left behind, and retained within a septum covered vial. Moreover, if there is an insufficient amount of the specimen available it may not be possible to pick it up from the vial in the first place. Present day automatic fluid injectors, notably the probe assemblies of such instruments are simply unable to pick up and deliver every last bit of the fluid specimen from the vial. Nor, where there is an insufficient amount of the specimen available, is it possible to pick it up and deliver same to the syringe. This is particularly unfortunate, for in many scientific and medical research situations only small, and infinitesmal quantities of a fluid specimen can be obtained from a source in the first place. There is thus a need for automatic fluid injeotors which are capable of picking up minute amounts of an available specimen, and for picking up greater amounts of the fluid specimens delivered by the septum covered vials for subsequent injection.